Preparation and properties of soluble and colorless fluorine-containing photoreactive polyimide precursors

Photoreactive polyimide precursors, which are readily soluble in common organic solvents and optically transparent at light of 365 nm wavelength (i‐line), similar to aliphatic polyimide precursors, were obtained by polycondensation of biphenyltetracarboxylic dianhydride (BPDA) and fluorine‐containing diamine compounds. In particular, the polyimide precursor prepared from 2,2 bis(3‐amino‐4‐methylphenyl) hexatluoropropane showed high solubility in common organic solvents and complete transparence at i‐line wavelength. A 3 μm thick film of the polyimide precursor on a silicon wafer was exposed and developed, and offered high resolution (0.5μm line) patterns with an aspect ratio of 6.0. This polymide precursor swells very little in the developing solvent, resulting in the high resolution. Conversion of polyamic acid to polyimide at several curing temperatures was observed by infrared spectrophotometer and thermogravimetry.